Tensilon test evaluates the response of muscles to the drug Tensilon (edrophonium chloride) in order to aid in the diagnosis of myasthenia gravis, a chronic disease in which the muscles weaken due to an impaired ability to respond to nerve signals.

To stimulate a muscle, nerve cells release a chemical messenger—the neurotransmitter acetylcholine—which is later broken down by the enzyme acetylcholinesterase. In people with myasthenia gravis, there are a reduced number of receptors for acetylcholine and the chemical is degraded before it can fully activate a muscle. Tensilon blocks the action of acetylcholinesterase, and thus can prolong muscle stimulation and temporarily improve muscle strength. An increase in muscle strength after an injection of Tensilon strongly suggests a diagnosis of myasthenia gravis.

Purpose of the Tensilon Test

  • To assist in the diagnosis of myasthenia gravis
  • To help differentiate between a myasthenic crisis (a worsening of the disease that necessitates therapy with anticholinesterase drugs) and a cholinergic crisis (caused by an overdose of anticholinesterase drugs). Both conditions are marked by severe muscle weakness and breathing difficulty.
  • To monitor oral anticholinesterase therapy

Who Performs It

  • A physician

Special Concerns

  • A number of medications, including prednisone, anticholinergics, procainamide, quinidine, and muscle relaxants, can interfere with test results.
  • Because Tensilon can produce certain adverse reactions, people with low blood pressure, slow heart rate, sleep apnea (temporary cessation of breathing during sleep), or mechanical obstruction of the intestine or urinary tract may not be candidates for this test.
  • In some cases, the drug Prostigmin (neostigmine)—used for the treatment of myasthenia gravis—is also administered to confirm a positive diagnosis established by the Tensilon test.

Before the Tensilon Test

  • Report to your doctor any medications, herbs, and supplements that you are taking. You may be advised to discontinue certain of these agents before the test. In general, do not take any medication within 4 hours of the procedure.
  • An intravenous (IV) needle or catheter is inserted into a vein in your arm immediately before the test begins.

What You Experience

To diagnose myasthenia gravis:

  • A small dose of Tensilon is injected through the IV line. You may be asked to perform certain exercises, such as counting toward 100 until your voice diminishes or holding your arms above your shoulders until they drop. After your muscles have been fatigued, a larger dose of Tensilon is given.
  • You will then be asked to perform some repetitive movements, such as opening and closing your eyes and crossing and uncrossing your legs, while the examiner looks for an increase in muscle strength. If the drug does not restore power to your muscles within 1 or 2 minutes, the dose is increased. The test may be repeated 3 to 4 times.
  • The procedure takes about 15 to 30 minutes.

To differentiate between a myasthenic and a cholinergic crisis:

  • A small amount of Tensilon is infused through the IV line, and the dose is gradually increased while the examiner observes you for signs of improved muscle strength (indicating a myasthenic crisis) or worsening muscle weakness (suggesting a cholinergic crisis).
  • If the test confirms a myasthenic crisis, the drug neostigmine is given immediately. If you are having a cholinergic crisis, the drug atropine is administered.
  • The procedure takes about 15 to 30 minutes.

To assess oral anticholinesterase therapy:

  • Tensilon is infused through the IV line 1 hour after you take your last dose of anticholinesterase medication, and you are carefully observed for muscle response and any adverse reactions.
  • The procedure takes about 15 to 30 minutes.

Risks and Complications

  • Tensilon may produce side effects such as nausea, abdominal discomfort, dizziness, blurred vision, fainting, breathing failure and rapid, frequent blinking of the eyelids.
  • Less often, the drug may cause potentially serious complications, including respiratory failure and heart rhythm abnormalities, in sensitive individuals. Appropriate resuscitation equipment is kept nearby to treat such adverse reactions.

After the Tensilon Test

  • The effects of Tensilon subside quickly and are completely gone after 30 to 60 minutes.
  • You may resume your normal activities and any medications that were withheld before the test, according to your doctor’s instructions.
  • Blood may collect and clot under the skin (hematoma) at the IV infusion site; this is harmless and will resolve on its own. For a large hematoma that causes swelling and discomfort, apply ice initially; after 24 hours, use warm, moist compresses to help dissolve the clotted blood.


  • The doctor will evaluate the results to determine if they support a diagnosis of myasthenia gravis; if you are experiencing a myasthenic or a cholinergic crisis; or if an adjustment in your anticholinesterase therapy is necessary.
  • If a definitive diagnosis can be made, treatment will be started or the dose of your current medication will be modified.
  • In some cases, additional tests, such as electromyography, will be needed to confirm a diagnosis of myasthenia gravis.


The Johns Hopkins Consumer Guide to Medical Tests

Simeon Margolis, M.D., Ph.D., Medical Editor

Updated by Remedy Health Media

Publication Review By: the Editorial Staff at Healthcommunities.com

Published: 24 Jan 2012

Last Modified: 23 Oct 2014